In recent years, there has been proposed systems performing various types of processing using an eye gaze direction of a subject (e.g., driver) that has been detected by an eye gaze direction detection apparatus. For example, there has been proposed many systems that uses the eye gaze direction detection apparatus, such as a detection apparatus for detecting inattentive driving and drowsy driving, and a human-machine interface (HMI) to manipulate an intelligent panel or the like based on an eye gaze.
In addition, there have been proposed various methods of eye gaze direction detection in the eye gaze direction detection apparatus. One of well-known methods is a corneal reflection method. In the corneal reflection method, an eye of a detection subject is irradiated with light of an infrared light-emitting diode (infrared LED), and an eye gaze direction is detected based on a positional relationship between a reflected image on the corneal surface of the eye and the pupil.
The eye gaze direction detection performed by the eye gaze direction detection apparatus generally involves detection errors resulting from individual differences of subjects. It is therefore necessary to ensure detection accuracy by executing so-called calibration for correcting detection error of each subject. In addition, even in a case of an identical subject, if the environment varies with time elapsed from previous calibration, detection error may be generated again. It is therefore desirable to execute calibration periodically.
The calibration performed by an eye gaze direction detection apparatus basically requires the measurement of 2 or more reference points. As the number of measured reference points increases, variations in eye gaze direction detection information are more leveled, and the calibration accuracy improves accordingly. For example, in an apparatus having a quadrangular display unit, it is generally considered desirable to promptly perform calibration of eye gaze direction detection information especially at 4 points near the corner portions and the center point of the display unit which is the intersection of diagonal lines.
However, measurement of a lot of reference points (e.g., 5 points in the above-described example) requires manipulation bothersome for a subject. For example, the subject is required to turn eyes on each of 5 predefined reference points, which puts a burden on the subject. Thus, an apparatus to automatically execute calibration without intention of a subject is demanded. Such an apparatus is proposed in the following documents.
For example, in the apparatuses proposed in Patent Documents 1 and 2, calibration is automatically executed without intention of a driver by using vehicle equipment as a gaze target object serving as a reference point.
Here, examples of the vehicle equipment used as a gaze target object include an inner rear view mirror, a sideview mirror, a navigation system, an air conditioner, a head-up display, and the like.
In Patent Document 1, an eye gaze direction of a driver is detected, and based on the result, vehicle equipment at which the driver is gazing is estimated. Then, the direction of the vehicle equipment viewed from the driver is predefined as a reference of an eye gaze direction, and calibration is executed based on the difference between the reference eye gaze direction and an eye gaze direction detected by an eye gaze direction detection apparatus. In addition, in Patent Document 2, calibration of an eye gaze direction detection apparatus is executed by associating an eye gaze obtained when a driver is manipulating each device, with the position of a corresponding manipulated device. In addition, Patent Document 2 also discloses a case of estimating, based on the distribution state of gaze points of the driver, that the gaze target object exists at the center of the distribution state.